In a known tool turret of the type to which the invention relates, an example of which is shown in German Pat. No. 16 27 051, a cam drive is provided for disengaging facing gear teeth, and another cam drive is provided for engaging the facing teeth. In this apparatus, the rotating head must be lifted out during the disengagement of the teeth and reinserted for reengagement thereof, so that the teeth will mesh again. The cam drive for disengaging the teeth includes an axial cam which works on the rotating head through a lug and a multiple-disc brake which creates the danger of force being applied excessively to one side. The cam drive for engaging of the teeth includes a radial cam which acts on gear teeth through a toggle lever mounted on the rotating head. This apparatus for selectively engaging and disengaging the facing teeth is very costly and occupies a considerable amount of space.
In another known tool turret shown in German Auslegeschrift No. 28 49 167, the cam drive has a member with an annular groove into which fits a guide member which is attached to a lever. A control element which rotatably supports the member with the annular groove in it is mounted on an axis parallel with the axis of the rotating head. The axis of the rotating head passes through the annular lever which acts on its shaft by means of a toggle lever coupling against the force of a spring when the gear teeth arrangement is to be engaged. This embodiment of the tool turret requires two shafts arranged side-by-side and, therefore, also uses much space and is expensive.
A multiple tool holder for machine tools having an annular locking part is also known, an embodiment of this being shown in German Offenlegungeschrift No. 27 41 907 and U.S. Pat. No. 4,202,227. This locking apparatus has a locking part with teeth on a facing side and axial cams on its other facing side by which the locking part can be axially forced against the bias of a spring. The other teeth of the facing teeth cooperating with those mounted on the locking part, and belonging to the facing gear teeth, are mounted on the rotating head and on a stationary part coaxial therewith. The facing cams on the locking part and on the stationary part of the multiple tool holder are permanently under spring bias, which creates increased frictional resistance.